f :: [[(a,[b])]] -> Int
f [(x,xs):[y,ys]]            = 0
f ([_]:[(x,[xs])]:[y,ys]:[]) = 1
f ([(x,y:_:[])]:[])          = 2

x0 :: [[(Bool, [Int])]]
x0 = [[(True,[2,4,6]),(True,[2,4,6]),(True,[2,4,6])]]

x1 :: [[(Char,[Int])]]
x1 = [[('a',[2])],  [('B',[2])],  [('a',[3]), ('D',[4])]]

x2 :: [[(Int, String)]]
x2 = [[(1, "ab")]]


letterize :: String -> [String]
letterize [] = []
letterize asd = [head asd]:letterize(tail asd)

swapElems :: [[a]] -> [[a]]
swapElems [] = []
swapElems ([x]:xs) = ([x]: swapElems xs)
swapElems ((st:nd:ys):xs) = ((nd:st:ys) : swapElems xs)